The structures, distributions, and functions of molecules of importance in the nervous system are being studied. Several cDNAs that encode neurotransmitter receptors have been isolated. In addition, cDNAs encoding a glycine transporter and the vesicular monoamine transporter have been cloned. The distributions of mRNAs to which the above DNAs are complementary have been or are being determined by means of in situ hybridization histochemistry (ISHH) as have the distributions of other mRNAs (e.g., peptide processing proteases, components of second messenger systems). Expression of cloned cDNAs has allowed functional studies to be undertaken.